Water treatment system and method

ABSTRACT

A method of treatment of liquid including supplying liquid to be treated to at least one liquid treatment module having a liquid inlet, a permeate outlet and a brine outlet, monitoring liquid pressure within the at least one liquid treatment module and upon exceedance of a liquid pressure threshold in the at least one liquid treatment module, reducing the liquid pressure in the at least one liquid treatment module by performing at least one of the following functions: opening a liquid pressure reducing valve at the brine outlet, increasing a liquid volume output of a circulation pump which removes brine from the at least one liquid treatment module, equilibrating liquid pressures between a liquid pressure inside the at least one liquid treatment module and inside a liquid feed tank and opening a liquid pressure reducing valve at the liquid inlet.

REFERENCE TO RELATED APPLICATIONS

Reference is hereby made to the following patent applications of thepresent inventor, the disclosures of which are hereby incorporated byreference:

U.S. patent application Ser. No. 13/603,028, filed Sep. 4, 2012,entitled “SYSTEM AND METHOD FOR DESALINATION OF WATER”, published asU.S. Patent Publication No. 2014/0061129;

U.S. patent application Ser. No. 14/145,068, filed Dec. 31, 2013,entitled “SYSTEM AND METHOD FOR DESALINATION OF WATER”, published asU.S. Patent Publication No. 2014/0110337; and

PCT Patent Application No. PCT/IL2013/050744, filed Sep. 2, 2013,entitled SYSTEM AND METHOD FOR TREATMENT OF WATER, published asInternational Publication No. WO 2014/037940.

FIELD OF THE INVENTION

The present invention relates to water treatment systems and methods.

BACKGROUND OF THE INVENTION

Various types of water treatment systems and methods are known.

SUMMARY OF THE INVENTION

The present invention seeks to provide improved water treatment systemsand methods. There is thus provided in accordance with a preferredembodiment of the present invention a method of treatment of liquidincluding supplying liquid to be treated to at least one liquidtreatment module employing at least one of reverse osmosis andnanofiltration membranes, the at least one module having a liquid inlet,a permeate outlet and a brine outlet, monitoring liquid pressure withinthe at least one liquid treatment module and upon exceedance of a liquidpressure threshold in the at least one liquid treatment module,representing exceedence of a salinity threshold in the liquid therein,reducing the liquid pressure in the at least one liquid treatment moduleby performing at least one of the following functions: opening a liquidpressure reducing valve at the brine outlet, thereby reducing the liquidpressure at the brine outlet to a level above atmospheric pressure whichexceeds osmotic pressure of the liquid in the at least one liquidtreatment module, increasing a liquid volume output of a circulationpump which removes brine from the at least one liquid treatment moduleand supplies liquid to the water inlet from a liquid volume output attimes other than upon and immediately following the exceedance,equilibrating liquid pressures between a liquid pressure inside the atleast one liquid treatment module and inside a liquid feed tank andopening a liquid pressure reducing valve at the liquid inlet, therebyproviding a pressure reducing backflow liquid path from the liquid inletof the at least one liquid treatment module which bypasses a liquidpressure increasing pump upstream of the liquid inlet.

In accordance with a preferred embodiment of the present invention uponexceedance of a liquid pressure threshold in the at least one liquidtreatment module, representing exceedence of a salinity threshold in theliquid therein, the liquid pressure in the at least one liquid treatmentmodule is reduced by performing at least two of the following functions:opening a liquid pressure reducing valve at the brine outlet, therebyreducing the liquid pressure at the brine outlet to a level aboveatmospheric pressure which exceeds osmotic pressure of the liquid in theat least one liquid treatment module, increasing a liquid volume outputof a circulation pump which removes brine from the at least one liquidtreatment module and supplies liquid to the water inlet from a liquidvolume output at times other than upon and immediately following theexceedance, equilibrating liquid pressures between a liquid pressureinside the at least one liquid treatment module and inside a liquid feedtank and opening a liquid pressure reducing valve at the liquid inlet,thereby providing a pressure reducing backflow liquid path from theliquid inlet of the at least one liquid treatment module which bypassesa liquid pressure increasing pump upstream of the liquid inlet.

In accordance with a preferred embodiment of the present invention uponexceedance of a liquid pressure threshold in the at least one liquidtreatment module, representing exceedence of a salinity threshold in theliquid therein, the liquid pressure in the at least one liquid treatmentmodule is reduced by performing at least three of the followingfunctions: opening a liquid pressure reducing valve at the brine outlet,thereby reducing the liquid pressure at the brine outlet to a levelabove atmospheric pressure which exceeds osmotic pressure of the liquidin the at least one liquid treatment module, increasing a liquid volumeoutput of a circulation pump which removes brine from the at least oneliquid treatment module and supplies liquid to the water inlet from aliquid volume output at times other than upon and immediately followingthe exceedance, equilibrating liquid pressures between a liquid pressureinside the at least one liquid treatment module and inside a liquid feedtank and opening a liquid pressure reducing valve at the liquid inlet,thereby providing a pressure reducing backflow liquid path from theliquid inlet of the at least one liquid treatment module which bypassesa liquid pressure increasing pump upstream of the liquid inlet.

In accordance with a preferred embodiment of the present invention uponexceedance of a liquid pressure threshold in the at least one liquidtreatment module, representing exceedence of a salinity threshold in theliquid therein, the liquid pressure in the at least one liquid treatmentmodule is reduced by performing all of the following functions: openinga liquid pressure reducing valve at the brine outlet, thereby reducingthe liquid pressure at the brine outlet to a level above atmosphericpressure which exceeds osmotic pressure of the liquid in the at leastone liquid treatment module, increasing a liquid volume output of acirculation pump which removes brine from the at least one liquidtreatment module and supplies liquid to the water inlet from a liquidvolume output at times other than upon and immediately following theexceedance, equilibrating liquid pressures between a liquid pressureinside the at least one liquid treatment module and inside a liquid feedtank and opening a liquid pressure reducing valve at the liquid inlet,thereby providing a pressure reducing backflow liquid path from theliquid inlet of the at least one liquid treatment module which bypassesa liquid pressure increasing pump upstream of the liquid inlet.

There is also provided in accordance with another preferred embodimentof the present invention a method of treatment of liquid including:supplying at least one water treatment module including at least onemembrane and having a feed water inlet at a feed side of the at leastone membrane, a permeate outlet at a permeate side of the at least onemembrane and a brine outlet at a brine side of at least one membrane,pressurizing feed water supplied to the feed water inlet by employing apump which normally maintains a fixed output feed water volumenotwithstanding variations in water pressure at an outlet thereof, theenergy consumption of the pump being a function of the variations inwater pressure at the outlet, monitoring the water pressure at theoutlet of the pump and when a predetermined high pressure threshold isreached at the outlet of the pump, immediately making changes in thewater supply to the module, thereby to cause immediate lowering of thewater pressure at the outlet of the pump, to a pressure below theosmotic pressure at the feed side of part but not all of the module,thereby immediately reducing the energy consumption of the pump, therebyproviding an overall energy cost savings per unit of water treated.

There is further provided in accordance with yet another preferredembodiment of the present invention a method for treatment of liquid inat least one liquid treatment module including at least a high pressurepump and a circulation pump, the method including upon occurrence of anoperational threshold representing exceedence of a salinity threshold inthe at least one liquid treatment module, effecting the following:removing brine from the at least one liquid treatment module andreducing, at an enhanced speed, pressure of the liquid in the at leastone liquid treatment module by at least one of the following: opening apressure reducing valve downstream of the high pressure pump, increasingthe volume output of the circulation pump from its volume output whenfunctioning as a concentrate circulation pump to a higher volume outputwhen functioning as a feed water pump and passing liquid from downstreamof the high pressure feed pump to upstream of the high pressure feedpump.

Preferably, the passing liquid from downstream of the high pressure feedpump to upstream of the high pressure feed pump includes passing theliquid via a flow restrictor arranged in parallel to the high pressurefeed pump.

In accordance with a preferred embodiment of the present invention thepressure of the liquid in the at least one liquid treatment module isreduced at an enhanced speed by at least two of the following: opening apressure reducing valve downstream of the high pressure pump, increasingthe volume output of the circulation pump from its volume output whenfunctioning as a concentrate circulation pump to a higher volume outputwhen functioning as a feed water pump and passing liquid from downstreamof the high pressure feed pump to upstream of the high pressure feedpump. Alternatively, the pressure of the liquid in the at least oneliquid treatment module is reduced at an enhanced speed by all of thefollowing: opening a pressure reducing valve downstream of the highpressure pump, increasing the volume output of the circulation pump fromits volume output when functioning as a concentrate circulation pump toa higher volume output when functioning as a feed water pump and passingliquid from downstream of the high pressure feed pump to upstream of thehigh pressure feed pump.

Preferably, the liquid treatment module is a water treatment moduleincluding at least one of at least one reverse osmosis membrane and atleast one nanofiltration membrane and is operative for treatment of atleast one of sea water, brackish water and waste water.

There is even further provided in accordance with another preferredembodiment of the present invention a water treatment system including:at least one liquid treatment module operative to receive feed water ata water inlet thereof and to separate the feed water into permeate andconcentrate, the permeate constituting treated water, the at least oneliquid treatment module having a brine outlet for release of concentratewhose salinity is such that an operational threshold of the system isexceeded, a liquid pressure reducing valve at the brine outlet, a highpressure pump, operative to pressurize liquid to be treated received ata liquid feed inlet and to provide a pressurized feed water output tothe at least one liquid treatment module, a feed water flow rate sensorlocated upstream of the high pressure pump and providing a feed waterflow rate output, a pump controller receiving the feed water flow rateoutput and controlling the operation of the high pressure pump, a liquidpressure sensor for providing an output indication of liquid pressure atat least one of an inlet to the at least one liquid treatment module, anoutlet from the at least one liquid treatment module and within the atleast one liquid treatment module, a circulation pump which removesbrine from the at least one liquid treatment module and supplies liquidto the water inlet, a liquid feed tank, a system controller receiving atleast the output indication of liquid pressure within the at least oneliquid treatment module, the system controller being operative, uponexceedance of a liquid pressure threshold in the at least one liquidtreatment module, representing exceedence of a salinity threshold in theliquid therein, reducing the liquid pressure in the at least one liquidtreatment module by performing at least one of the following functions:opening the liquid pressure reducing valve at the brine outlet, therebyreducing the liquid pressure at the brine outlet to a level aboveatmospheric pressure which exceeds osmotic pressure of the liquid in theat least one liquid treatment module, increasing a liquid volume outputof the circulation pump, which removes brine from the at least oneliquid treatment module and supplies liquid to the water inlet from aliquid volume output at times other than upon and immediately followingthe exceedance, equilibrating liquid pressures between a liquid pressureinside the at least one liquid treatment module and inside the liquidfeed tank and opening a liquid pressure reducing valve at the liquidinlet, thereby providing a pressure reducing backflow liquid path fromthe liquid inlet of the at least one liquid treatment module whichbypasses the high pressure pump upstream of the liquid inlet.

In accordance with a preferred embodiment of the present invention thesystem controller is operative, upon exceedance of a liquid pressurethreshold in the at least one liquid treatment module, representingexceedence of a salinity threshold in the liquid therein, reducing theliquid pressure in the at least one liquid treatment module byperforming at least two of the following functions: opening the liquidpressure reducing valve at the brine outlet, thereby reducing the liquidpressure at the brine outlet to a level above atmospheric pressure whichexceeds osmotic pressure of the liquid in the at least one liquidtreatment module, increasing a liquid volume output of the circulationpump, which removes brine from the at least one liquid treatment moduleand supplies liquid to the water inlet from a liquid volume output attimes other than upon and immediately following the exceedance,equilibrating liquid pressures between a liquid pressure inside the atleast one liquid treatment module and inside the liquid feed tank andopening a liquid pressure reducing valve at the liquid inlet, therebyproviding a pressure reducing backflow liquid path from the liquid inletof the at least one liquid treatment module which bypasses the highpressure pump upstream of the liquid inlet.

Alternatively, the system controller is operative, upon exceedance of aliquid pressure threshold in the at least one liquid treatment module,representing exceedence of a salinity threshold in the liquid therein,reducing the liquid pressure in the at least one liquid treatment moduleby performing at least three of the following functions: opening theliquid pressure reducing valve at the brine outlet, thereby reducing theliquid pressure at the brine outlet to a level above atmosphericpressure which exceeds osmotic pressure of the liquid in the at leastone liquid treatment module, increasing a liquid volume output of thecirculation pump, which removes brine from the at least one liquidtreatment module and supplies liquid to the water inlet from a liquidvolume output at times other than upon and immediately following theexceedance, equilibrating liquid pressures between a liquid pressureinside the at least one liquid treatment module and inside the liquidfeed tank and opening a liquid pressure reducing valve at the liquidinlet, thereby providing a pressure reducing backflow liquid path fromthe liquid inlet of the at least one liquid treatment module whichbypasses the high pressure pump upstream of the liquid inlet.

In another alternative embodiment, the system controller is operative,upon exceedance of a liquid pressure threshold in the at least oneliquid treatment module, representing exceedence of a salinity thresholdin the liquid therein, to reduce the liquid pressure in the at least oneliquid treatment module by performing all of the following functions:opening the liquid pressure reducing valve at the brine outlet, therebyreducing the liquid pressure at the brine outlet to a level aboveatmospheric pressure which exceeds osmotic pressure of the liquid in theat least one liquid treatment module, increasing a liquid volume outputof the circulation pump, which removes brine from the at least oneliquid treatment module and supplies liquid to the water inlet from aliquid volume output at times other than upon and immediately followingthe exceedance, equilibrating liquid pressures between a liquid pressureinside the at least one liquid treatment module and inside the liquidfeed tank and opening a liquid pressure reducing valve at the liquidinlet, thereby providing a pressure reducing backflow liquid path fromthe liquid inlet of the at least one liquid treatment module whichbypasses the high pressure pump upstream of the liquid inlet.

There is yet further provided in accordance with still another preferredembodiment of the present invention a water treatment system includingat least one water treatment module including at least one membrane andhaving a feed water inlet at a feed side of the at least one membrane, apermeate outlet at a permeate side of the at least one membrane and abrine outlet at a brine side of at least one membrane, a high pressurepump, which normally maintains a fixed output feed water volumenotwithstanding variations in water pressure at an outlet thereof, asystem controller receiving at least the output indication of liquidpressure within the at least one liquid treatment module, the systemcontroller being operative, upon exceedance of a liquid pressurethreshold in the at least one liquid treatment module, representingexceedence of a salinity threshold in the liquid therein, to reduce theliquid pressure in the at least one liquid treatment module byperforming at least one of the following functions: pressurizing feedwater supplied to the feed water inlet by employing the high pressurepump, the energy consumption of the high pressure pump being a functionof the variations in water pressure at the outlet, monitoring the waterpressure at the outlet of the high pressure pump and when apredetermined high pressure threshold is reached at the outlet of thehigh pressure pump, immediately making changes in the water supply tothe at least one liquid treatment module, thereby to cause immediatelowering of the water pressure at the outlet of the high pressure pump,to a pressure below the osmotic pressure at the feed side of part butnot all of the at least one liquid treatment module, thereby immediatelyreducing the energy consumption of the high pressure pump, therebyprovide an overall energy cost savings per unit of water treated.

There is still further provided in accordance with yet another preferredembodiment of the present invention a water treatment system includingat least one water treatment module including at least one membrane andhaving a feed water inlet at a feed side of the at least one membrane, apermeate outlet at a permeate side of the at least one membrane and abrine outlet at a brine side of at least one membrane, a high pressurepump, which normally maintains a fixed output feed water volumenotwithstanding variations in water pressure at an outlet thereof, apressure reducing valve downstream of the high pressure feed pump, acirculation pump, a system controller receiving at least the outputindication of liquid pressure within the at least one liquid treatmentmodule, the system controller being operative, upon exceedance of aliquid pressure threshold in the at least one liquid treatment module,representing exceedence of a salinity threshold in the liquid therein,to reduce the liquid pressure in the at least one liquid treatmentmodule by performing at least one of the following functions: uponoccurrence of an operational threshold representing exceedence of asalinity threshold in the at least one liquid treatment module,effecting the following: removing brine from the at least one liquidtreatment module and reducing, at an enhanced speed, pressure of theliquid in the at least one liquid treatment module by at least one ofthe following: opening the pressure reducing valve downstream of thehigh pressure feed pump, increasing the volume output of the circulationpump from its volume output when functioning as a concentratecirculation pump to a higher volume output when functioning as a feedwater pump and passing liquid from downstream of the high pressure feedpump to upstream of the high pressure feed pump.

Preferably, the water treatment system also includes a flow restrictorarranged in parallel to the high pressure feed pump and the passingliquid from downstream of the high pressure feed pump to upstream of thehigh pressure feed pump includes passing the liquid via the flowrestrictor.

In accordance with a preferred embodiment of the present invention thepressure of the liquid in the at least one liquid treatment module isreduced at an enhanced speed by at least two of the following: openingthe pressure reducing valve downstream of the high pressure feed pump,increasing the volume output of the circulation pump from its volumeoutput when functioning as a concentrate circulation pump to a highervolume output when functioning as a feed water pump and passing liquidfrom downstream of the high pressure feed pump to upstream of the highpressure feed pump. Alternatively, the pressure of the liquid in the atleast one liquid treatment module is reduced at an enhanced speed by atleast three of the following: opening the pressure reducing valvedownstream of the high pressure feed pump, increasing the volume outputof the circulation pump from its volume output when functioning as aconcentrate circulation pump to a higher volume output when functioningas a feed water pump and passing liquid from downstream of the highpressure feed pump to upstream of the high pressure feed pump.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully fromthe following detailed description, taken in conjunction with thedrawings in which:

FIG. 1 is a simplified illustration of a system for water treatmentconstructed and operative in accordance with a preferred embodiment ofthe present invention;

FIGS. 2A and 2B are simplified illustrations of examples of periodicvariations in feed water pressure and osmotic pressure in embodiments ofthe system of FIG. 1, each showing a distinction from the prior art;

FIGS. 3A, 3B. 3C and 3D are simplified illustrations of liquid flows inthe system of FIG. 1 at various stages in the periodic variation in feedwater pressure and osmotic pressure shown in FIG. 2A in accordance withone embodiment of the present invention;

FIGS. 4A, 4B, 4C and 4D are simplified illustrations of liquid flows inthe system of FIG. 1 at various stages in the periodic variation in feedwater pressure and osmotic pressure shown in FIG. 2A in accordance withanother embodiment of the present invention;

FIGS. 5A, 5B and 5C are simplified illustrations of liquid flows in thesystem of FIG. 1 at various stages in the periodic variation in feedwater pressure and osmotic pressure shown in FIG. 2A in accordance withstill another embodiment of the present invention;

FIGS. 6A, 6B, 6C and 6D are simplified illustrations of liquid flows inthe system of FIG. 1 at various stages in the periodic variation in feedwater pressure and osmotic pressure shown in FIG. 2B in accordance withyet another embodiment of the present invention;

FIGS. 7A, 7B, 7C and 7D are simplified illustrations of liquid flows inthe system of FIG. 1 at various stages in the periodic variation in feedwater pressure and osmotic pressure shown in FIG. 2B in accordance witha further embodiment of the present invention;

FIGS. 8A, 8B, 8C and 8D are simplified illustrations of liquid flows inthe system of FIG. 1 at various stages in the periodic variation in feedwater pressure and osmotic pressure shown in FIG. 2B in accordance withstill a further embodiment of the present invention:

FIGS. 9A, 9B, 9C and 9D are simplified illustrations of liquid flows inthe system of FIG. 1 at various stages in the periodic variation in feedwater pressure and osmotic pressure shown in FIG. 2A in accordance withyet a further embodiment of the present invention;

FIGS. 10A, 10B, 10C and 10D are simplified illustrations of liquid flowsin the system of FIG. 1 at various stages in the periodic variation infeed water pressure and osmotic pressure shown in FIG. 2A in accordancewith an alternative embodiment of the present invention; and

FIGS. 11A, 11B, 11C and 11D are simplified illustrations of liquid flowsin the system of FIG. 1 at various stages in the periodic variation infeed water pressure and osmotic pressure shown in FIG. 2B in accordancewith a further embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference is now made to FIG. 1, which is a simplified illustration of aliquid treatment system constructed and operative in accordance with apreferred embodiment of the present invention, and to FIGS. 2A and 2B,which are simplified time-line illustrations of examples of theoperation of the system of FIG. 1, wherein seawater is beingdesalinated.

The liquid treatment system of FIG. 1 comprises at least one liquidtreatment module, preferably water treatment module 100, comprisingreverse osmosis membranes and/or nanofiltration membranes. The system ofFIG. 1 is operative for treatment of liquid to be treated, such as feedwater, which may be, for example, sea water, brackish water or wastewater.

Water treatment module 100 is described in applicant's U.S. patentapplication Ser. No. 13/603,028, filed Sep. 4, 2012 and entitled SYSTEMAND METHOD FOR DESALINATION OF WATER, and published as U.S. PublishedPatent Application No. 2014/0061129 on Mar. 6, 2014, the disclosure ofwhich is hereby incorporated by reference. FIG. 2A in U.S. patentapplication Ser. No. 13/603,028 illustrates a water treatment module,here designated by reference numeral 100.

For the purposes of the description which follows, the followingdefinitions will be employed:

feed water—water to be treated by the system, such as saline solution,sea water, brackish water or waste water;

mixed feed water—water supplied to water treatment module 100, which mayinclude feed water and water that was previously treated in the watertreatment module 100 and is being resupplied to the water treatmentmodule for further treatment;

module feed side water—water at a feed side, as distinguished from apermeate side, of module 100. The salinity of the module feed side waterincreases as the module feed side water passes through the module froman initial salinity, which represents the salinity of the mixed feedwater, to a concentrate salinity, which represents the salinity of theconcentrate output at an output of the feed side, as distinguished fromthe permeate side, of module 100.

It is an inherent feature of water treatment modules 100 that theosmotic pressure at the feed side thereof increases over time as thesalinity at the feed side increases until such time as the salinity atthe feed side is reduced, thereby reducing the osmotic pressure. Asdescribed hereinbelow, the salinity of the mixed feed water at the feedside is preferably reduced by supplying only feed water instead of amixture of feed water and recirculated concentrate.

An increase in osmotic pressure requires a corresponding increase inwater pressure at the feed side of the module 100 in order to maintainpermeate production. This increase is provided automatically by a highpressure pump 102, preferably operative to pressurize the liquid to betreated to typical pressures of approximately 15 bar for brackish waterand up to approximately 70 bar for sea water.

High pressure pump 102 may be any suitable type of pump, such as apositive displacement pump. An example of a preferred positivedisplacement pump is a Danfoss APP 21-43 high pressure pump,commercially available from Danfoss A/S Nordborgvej 81, 6430 Nordborg,Denmark. High pressure pump 102 is preferably controlled by the outputof a feed water flow rate sensor 104 upstream of pump 102, which isreceived by a pump controller 106, preferably an ABB ACS800-U1controller, commercially available from ABB Inc. MS 3L7 29801 EuclidAve, Wickliffe, Ohio 44092-2530, USA.

Preferably, a mixed feed water pressure sensor 108 is provided at thefeed side of module 100. A typical graph of mixed feed water pressure asmeasured by pressure sensor 108 over time and verses the osmoticpressure at the feed side of the module 100 appears in an enlargementforming part of FIG. 1 and in FIGS. 2A and 2B. Alternatively oradditionally, a water pressure sensor may be provided at a suitablelocation within module 100 or at a module outlet for measuring thepressure of liquid flowing therethrough.

The variation of feed water pressure over time typically has aperiodicity of a few minutes, typically between 3-30 minutes in seawaterdesalination and possibly longer in brackish water desalination.

As seen in FIG. 1, water treatment module includes a plurality ofpressure vessels 110 arranged in parallel. Each pressure vessel 110preferably includes a plurality of membrane elements 112, typicallyeight in number, only four being shown in the drawing for the sake ofconciseness. Pressure vessels 110 are commercially available fromvarious vendors, for example BEL Composite Industries Ltd, IndustrialZone, Kiryat Yehudit. P.O.B. 4, 84100 Beer Sheva, Israel, and membraneelements 112 are commercially available from various vendors, forexample LG NanoH2O, 750 Lairport Street, El Segundo, CA 90245.

Liquid to be treated is supplied at a liquid feed inlet and ispressurized by high pressure pump 102, preferably operative topressurize the liquid to be treated to typical pressures ofapproximately 15 bar for brackish water and up to approximately 70 barfor sea water.

The liquid to be treated, hereinafter referred to as feed water, whereinthe definition of “feed water” encompasses, inter alia, saline solution,brackish water, sea water and waste water, is supplied via a feedmanifold 114 to the parallel pressure vessels 110. Treated water,hereinafter referred to as permeate, wherein the definition of“permeate” encompasses, inter alia, “product water”, from each ofpressure vessels 110, is preferably supplied via a permeate manifold 116to a permeate outlet 118.

Concentrate from each of pressure vessels 110 is preferably supplied viaa concentrate manifold 120 to a recirculation conduit 122, which directsthe concentrate back to feed manifold 114, downstream of pump 102, via arecirculation control valve 124 by employing a circulation pump 126. Aconcentrate pressure sensor 128, a concentrate conductivity sensor 129and a concentrate flow rate sensor 130 are preferably provideddownstream of concentrate manifold 120.

Concentrate from module 100 may also be provided from pressure vessels110 via concentrate manifold 120 to a brine outlet 132 via a brineoutlet control valve 134 for flushing. Concentrate that exits module 100and is not recirculated is referred to herein as brine. Preferably, thesalinity of the brine that is flushed is greater than the salinity ofthe concentrate that is recirculated via conduit 122.

In some embodiments of the present invention, brine from each ofpressure vessels 110 may be supplied from concentrate manifold 120 viaan auxiliary brine replacement conduit 136, an auxiliary tank feedconduit 138 and an auxiliary brine replacement control valve 140 to anauxiliary feed water tank 142. Preferably, the salinity of the brinesupplied to auxiliary feed water tank 142 exceeds the salinity of theconcentrate that is recirculated via conduit 122.

It is appreciated that, as described further hereinbelow, the decisionto recirculate the liquid as concentrate or to flush the liquid as brinemay be a function of the salinity of the liquid, a function of thepressure of the liquid, a function of a rate of accumulation of foulantson membrane elements, a system energy efficiency rating, or may be basedon a predetermined time schedule or any other suitable method.Additionally or alternatively, the selection of the threshold may bepredetermined to be a suitable threshold which will avoid or minimizeprecipitation of foulants on the membrane elements 112 in module 100.

During the flushing of brine, the recirculation control valve 124 isclosed. The auxiliary feed water tank 142 is preferably filled, prior tothe opening of auxiliary brine replacement control valve 140, with feedwater by an auxiliary feed water pump 144. Brine driven by circulationpump 126 drives the feed water from auxiliary feed water tank 142 tofeed manifold 114 via an auxiliary feed water conduit 146 and anauxiliary feed water control valve 148. An auxiliary water flow sensor150 is provided upstream of auxiliary feed water tank 142. After fullreplacement of brine by feed water in module 100, the recirculationcontrol valve 124 is opened and auxiliary brine replacement controlvalve 140 and auxiliary feed water control valve 148 are closed. Thenauxiliary feed water pump 144 fills auxiliary feed water tank 142 withfeed water, which drives the brine to an auxiliary brine outlet 152 viaan auxiliary brine outlet tank control valve 154.

It is appreciated that, alternatively, elements 136-154 may be obviated.

In some embodiments of the present invention, water pressure at the feedside of the module 100 may be quickly reduced at desired points in timeby operation of a recycle conduit control valve 156 to redirect feedwater from downstream of high pressure feed pump 102 to upstream of pump102 through a conduit 158 and preferably through a flow restrictor 160,which limits the pressure reduction to a pressure above atmosphericpressure, which pressure exceeds the osmotic pressure of the feed waterat the feed side of module 100.

In accordance with a preferred embodiment of the present invention thereis provided a Feed Pressure Management (FPM) Controller 162, whichcontrols the operation of the high pressure feed pump 102, circulationpump 126, auxiliary feed water pump 144, recirculation control valve124, brine outlet control valve 134, auxiliary brine replacement controlvalve 140, auxiliary feed water control valve 148, auxiliary brineoutlet tank control valve 154, and recycle conduit control valve 156 foradjusting the pressure at which desalination takes place at the at leastone water treatment module.

As seen in FIGS. 2A and 2B, which will be described in detailhereinbelow, and refer to examples wherein seawater is beingdesalinated, periodic variations in the feed water pressure during watertreatment correspond to periodic variations in the osmotic pressure,which corresponds to the salinity of the feed water supplied to module100, as measurable by a conductivity sensor (not shown) typicallydownstream of pressure sensor 108.

Control over the variation of the feed water pressure may be achieved invarious ways, such as according to the flow rate measured by flow sensor104 and, alternatively or additionally, according to the salinity of thewater being supplied to the feed side of the module 100, which mayinclude feed water received from pump 102, recirculated water receivedfrom recirculation conduit 122, auxiliary feed water received viaauxiliary conduit 146 and combinations thereof.

Alternatively, the feed pressure may be varied in accordance with apredetermined time schedule. As a further alternative, the desired feedpressure may be reached by employing recycle conduit 158 with or withoutflow restrictor 160. Other alternative methodologies for control overthe variation of the feed pressure may be employed.

FPM controller 162 is operative to periodically open and closerecirculation control valve 124, brine outlet control valve 134,auxiliary brine replacement control valve 140, auxiliary feed watercontrol valve 148, auxiliary brine outlet tank control valve 154 andrecycle conduit control valve 156 in accordance with a predeterminedtime schedule or alternatively, for example, in response to eithersensed salinity of the concentrate, for example as per an output ofsensor 129, or exceedance of a predetermined maximum feed pressurethreshold, for example as per an output of sensor 108 or sensor 128.

FPM controller 162 is also preferably operative to periodically activateauxiliary feed water pump 144 and may also be operative to change theflow rate of circulation pump 126. Other alternative algorithms forcontrol of opening and closing recirculation control valve 124, brineoutlet control valve 134, auxiliary brine replacement control valve 140,auxiliary feed water control valve 148, auxiliary brine outlet tankcontrol valve 154 and recycle conduit control valve 156, and for controlof the operation of the high pressure feed pump 102, circulation pump126 and auxiliary feed water pump 144 may be employed.

In some embodiments of the invention, once the concentration of theconcentrate increases to a predetermined level at which continued watertreatment is deemed not to be practicable, the FPM controller 162 opensauxiliary brine replacement control valve 140 and allows brine to flowfrom concentrate manifold 120, via auxiliary brine replacement conduit136 and auxiliary tank feed water conduit 138, to auxiliary feed watertank 142. In some embodiments of the invention, FPM controller 162 alsocloses recirculation control valve 124 at about the same time. Thevolume of the brine flowing out of the system may be measured byconcentrate flow rate sensor 130. Feed water that was in auxiliary feedwater tank 142 is driven by circulation pump 126 to flow via auxiliaryfeed water conduit 146 and auxiliary feed water control valve 148 tofeed manifold 114. Feed water, having salinity which is significantlylower than that of the brine, thus enters module 100.

Various methodologies for ensuring that the feed water pressure is aboveatmospheric pressure and above the osmotic pressure of the feed water atthe feed side of module 100 at all times are described hereinbelow withreference to FIGS. 2A & 2B and to FIGS. 3A-11D. Ensuring that the feedwater pressure remains above atmospheric pressure and above the osmoticpressure of the feed water at the feed side of module 100 preventsovershooting of the feed pressure when feed water from high pressurefeed pump 102 enters the module 100, which overshooting commonly occursin prior art systems.

It is appreciated that the term ‘overshooting’ as used herein refers tooperating the high pressure feed pump 102 at an excessively highpressure relative to the osmotic pressure of the feed water, which istypically caused when the controller causes the system to supply feedwater, as from auxiliary feed water tank 142, instead of recirculatedconcentrate to modules 100, without modifying the pressure of feed watersupplied via high pressure feed pump 102. The operation of the highpressure feed pump 102 at an excessively high pressure relative to theosmotic pressure of the feed water, increases the energy required tooperate the system.

In the description which follows, it is to be appreciated that thepressure values given for the various embodiments described hereinbelowand shown in FIGS. 2A & 2B are values associated with membrane sea waterdesalination. Different pressure values will apply to desalination ofbrackish water and other types of feed water.

In steady state normal operation of the system, prior to initiation of aperiodic process of replacing the concentrate in the water treatmentmodule 100 with feed water, brine outlet control valve 134, auxiliarybrine replacement control valve 140, auxiliary feed water control valve148, auxiliary brine outlet tank control valve 154 and recycle conduitcontrol valve 156 are all closed and recirculation control valve 124 isopen.

In this steady state normal operation, concentrate from concentratemanifold 120 is directed back to the input of feed manifold 114 viarecirculation conduit 122 and recirculation control valve 124, as shownin FIG. 1 by an arrow labeled CONCENTRATE representing the recirculationflow in recirculation conduit 122. In feed manifold 114, the concentrateis mixed with feed water, as shown in FIG. 1 by an arrow labeled MIXED,representing the mixed flow in the feed manifold 114, and the mixed flowenters pressure vessels 110 of module 100 for treatment. Theabove-described flow in steady state normal operation is represented insolid black lines in FIGS. 3A, 4A, 5A, 6A, 7A, 8A, 9A, 10A and 11A.

The feed pressure gradually increases as the salinity of the mixed waterbeing supplied to the membrane elements 112 increases. Once theconcentration of the concentrate increases to a predetermined level atwhich continued water treatment is deemed not to be practicable, theperiodic process of replacing the concentrate in the water treatmentmodule 100 with feed water is initiated. FIGS. 3A-11D illustrate varioustechniques for replacing the concentrate in the water treatment module100 with feed water at a pressure above atmospheric pressure, whichexceeds the osmotic pressure of the feed water at the feed side ofmodule 100 without causing overshooting.

Typically, the predetermined level of concentrate concentration deemednot to be practicable to continue treating, is based on one of a numberof operational considerations, such as rate of accumulation of foulantsand energy efficiency.

Reference in now made to FIG. 2A, which illustrates the periodicvariations in mixed feed water pressure as measured by pressure sensor108, and in the mixed feed water osmotic pressure estimated to exist atpressure sensor 108 when circulation pump 126 is operating at a normalpumping rate. The estimated mixed feed water osmotic pressure atpressure sensor 108 is generally a function of the salinity of the waterat the feed side of the membranes 112 in module 100.

Periodic variations in the mixed feed water pressure during watertreatment correspond to periodic variations in the salinity of the feedwater entering module 100, as measurable by the conductivity sensor,typically located downstream of pressure sensor 108. The y-axisrepresents pressure in seawater desalination, and the x-axis representtime. Dashed vertical lines ‘A’ represent points in time where athreshold, such as a maximum feed water pressure threshold, is reached.

When the threshold is reached, pressure vessels 110 are still filledwith concentrate, whose salt concentration continues to increase as itmoves through the pressure vessel. Therefore, both mixed feed waterosmotic pressure and mixed feed water pressure continue to increase,until feed water enters the pressure vessels 110 replacing theconcentrate therein. Typically, reaching the threshold causes the systemto begin the brine flushing process.

In FIGS. 2A and 2B, the mixed feed water osmotic pressure line 170represents the estimated osmotic pressure of the mixed feed water. Thus,when feed water from pump 102 is mixed with concentrate fromrecirculation conduit 122, the mixed osmotic pressure graduallyincreases as seen in the gradual slope of line 170. Once a threshold,such as a salinity threshold or a pressure threshold, is reached thecontroller 162 preferably begins the flushing process. During theflushing process, concentrate is not recirculated back to feed manifold114, thus only feed water enters feed manifold 114 and the mixed osmoticpressure decreases sharply, as shown in the sharp decline in line 170.

Line 175 in FIG. 2A illustrates the behavior of the mixed feed waterpressure in the prior art, represented by the teaching of U.S. Pat. No.8,025,804. Line 180 illustrates the mixed feed water pressure beingcontrolled by the controller such that the mixed feed water pressureneeded for reverse osmosis desalination process is maintained not onlyduring the gradual increase of mixed feed water pressure, whenconcentrate is being recirculated back to feed manifold 114, but also attimes of flushing the brine in pressure vessels 110 by feeding only feedwater without recirculated concentrate. The difference between line 175and line 180 illustrates the energy benefit of operation at lowerpressures for desalination of sea water, thus saving energy.

In both FIGS. 2A and 2B, line 190 illustrates the osmotic pressure ofthe module feed side water.

As described further hereinbelow, FIG. 2B is similar to FIG. 2A, exceptthat the values are provided for the embodiment where circulation pump126 is operating at a higher than normal pumping rate, generating ahigher flow.

Reference is now made to FIGS. 3A-3D, which are simplified illustrationsof water flows in a first embodiment of a water treatment system of thetype shown in FIG. 1.

FIG. 3A shows the flow during normal steady state operation of thesystem in solid black.

FIG. 3B shows, in solid black lines, the flow that takes place, once theconcentration of the concentrate increases to a predetermined level. Atthis stage, the FPM controller 162 opens auxiliary brine replacementcontrol valve 140, closes recirculation control valve 124 and opensauxiliary feed water control valve 148. Brine from concentrate manifold120 flows through auxiliary brine replacement conduit 136 and auxiliarybrine replacement control valve 140 via auxiliary tank feed conduit 138to auxiliary feed water tank 142. The auxiliary feed water tank 142 isfilled with feed water prior to the opening of auxiliary brinereplacement control valve 140, as described hereinbelow. The brineenters the auxiliary feed water tank 142 and drives feed water from tank142 to feed manifold 114 via auxiliary feed water conduit 146 andauxiliary feed water control valve 148.

It is noted that water in auxiliary feed water tank 142 may bemaintained at the same pressure as that of the brine, such as bymaintaining auxiliary brine replacement control valve 140 in an openstate as the water pressure in the system gradually increases.Alternatively, the water in the auxiliary feed water tank 142 may bemaintained at a pressure which is much lower than the pressure of thebrine but above atmospheric pressure by operation of auxiliary feedwater pump 144, as described hereinbelow.

During flushing, FPM controller 162 preferably opens recycle conduitcontrol valve 156, resulting in a water flow from a location downstreamof pump 102 to a location upstream of pump 102, optionally thorough arestrictor 160, thus lowering the feed water pressure at manifold 114 toa pressure above atmospheric pressure, which pressure exceeds theosmotic pressure of the feed water at the feed side of module 100.

Concentrate flow rate sensor 130 measures the cumulative volume of brineflowing from concentrate manifold 120 and thus measures the cumulativevolume of feed water entering feed manifold 114 via auxiliary feed waterconduit 146 and auxiliary feed water control valve 148, which replacesthe brine in module 100.

After complete replacement of brine with feed water in module 100, FPMcontroller 162 reopens recirculation control valve 124 and closesauxiliary brine replacement control valve 140, auxiliary feed watercontrol valve 148 and recycle conduit control valve 156, providing aliquid flow as shown in FIG. 3C, which may be identical to the liquidflow illustrated in FIG. 3A, in which the operation of circulation pump126 and of high pressure pump 102 supplies mixed feed water to module100.

Thereafter, FPM controller 162 periodically activates auxiliary feedwater pump 144 and opens auxiliary brine outlet tank control valve 154to flush all brine from auxiliary feed water tank 142 through anauxiliary brine outlet 152 to a location outside of the at least onewater treatment system, and to fill the auxiliary feed tank 142 withfeed water for future replacement of the brine in module 100. This flowis shown in solid black lines in FIG. 3D.

Following full replacement of brine with feed water in auxiliary feedwater tank 142, as measured by auxiliary flow sensor 150, FPM controller162 closes auxiliary brine outlet tank control valve 154 and terminatesoperation of auxiliary feed water pump 144.

Reference is now made to FIGS. 4A-4D, which are simplified illustrationsof water flows in a second embodiment of a water treatment system of thetype shown in FIG. 1.

Prior to initiation of removal of the concentrate from the module 100,brine outlet control valve 134, auxiliary brine replacement controlvalve 140, auxiliary feed water control valve 148 and recycle conduitcontrol valve 156 are closed and recirculation control valve 124 isopen. The concentrate from concentrate manifold 120 is directed back toinput of feed manifold 114 via recirculation conduit 122 andrecirculation control valve 124, as shown by an arrow labeledCONCENTRATE (FIG. 1), representing the recirculation flow in therecirculation conduit 122. In feed manifold 114, the concentrate ismixed with feed water, as shown by an arrow labeled MIXED (FIG. 1),representing the mixed flow in the feed manifold 114. Thus, a mixed flowenters pressure vessels 110 for further treatment. The water flow forthis stage is shown in a solid black line in FIG. 4A.

The feed pressure thereafter gradually increases, as the salinity of themixed water being supplied to membrane elements 112 increases, and theabove-described recirculation process continues.

Once the concentration of the concentrate reaches a threshold, such as apredetermined salinity level at which continued water treatment isdeemed not to be practicable, FPM controller 162 opens auxiliary brinereplacement control valve 140, which is approximately at atmosphericpressure, thus reducing the water pressure within module 100 to apressure between the pressure of the concentrate at module 100 and thepressure of the feed water in the auxiliary feed tank 142.

Immediately thereafter, FPM controller 162 closes recirculation controlvalve 124 and opens auxiliary feed water control valve 148. Feed waterfrom auxiliary feed tank 142 flows via auxiliary feed water conduit 146and feed water control valve 148 to feed manifold 114, as shown in FIG.4B, thus supplying feed water to module 100 at a pressure above theosmotic pressure of the feed water and slightly higher than the pressurerequired for reverse osmosis to occur.

Concentrate flow rate sensor 130 measures the cumulative volume of brineflowing from concentrate manifold 120, and thus measures the cumulativevolume of feed water entering feed manifold 114 via the auxiliary feedwater conduit 146 and the auxiliary feed water control valve 148, whichreplaces the brine in module 100.

After full replacement of the brine with feed water in module 100, FPMcontroller 162 reopens recirculation control valve 124, and closesauxiliary brine replacement control valve 140 and auxiliary feed watercontrol valve 148, providing a liquid flow as shown in FIG. 4C, whichmay be identical to the liquid flow illustrated in FIG. 4A, in which theoperation of high pressure pump 102 and the circulation pump 126supplies mixed feed water to module 100.

Thereafter, the FPM controller 162 periodically activates the auxiliaryfeed water pump 144 and opens auxiliary brine outlet tank control valve154 to flush all brine from auxiliary feed water tank 142 through anauxiliary brine outlet 152 to a location outside of the at least onewater treatment system and fill the auxiliary feed tank 142 with feedwater for further replacement of the brine in module 100 with feed wateras described hereinabove, as seen in FIG. 4D. Following full replacementof brine with feed water in auxiliary feed water tank 142, as measuredby auxiliary flow sensor 150, FPM controller 162 closes auxiliary brineoutlet tank control valve 154 and terminates operation of auxiliary feedwater pump 144.

Reference is now made to FIGS. 5A-5C, which are simplified illustrationsof water flows in another embodiment of a water treatment system of thetype shown in FIG. 1.

Prior to initiation of removal of the concentrate from module 100, brineoutlet control valve 134, auxiliary brine replacement control valve 140,auxiliary feed water control valve 148 and recycle conduit control valve156 are closed and recirculation control valve 124 is opened. Theconcentrate from concentrate manifold 120 is directed back to the inputof feed manifold 114 via recirculation conduit 122 and recirculationcontrol valve 124, as shown by an arrow labeled CONCENTRATE (FIG. 1),representing the recirculation flow in the recirculation conduit 122. Infeed manifold 114, the concentrate is mixed with feed water, as shown byan arrow labeled MIXED (FIG. 1) representing the mixed flow in the feedmanifold 114. Thus, a mixed flow enters pressure vessels 110 for furthertreatment. The water flow for this stage is shown in a solid black linein FIG. 5A.

The feed pressure thereafter gradually increases as the salinity of themixed water being supplied to the membrane elements 112 increases, andthe above-described recirculation process continues.

Once the concentration of the concentrate reaches a threshold, such as apredetermined salinity level at which continued water treatment isdeemed not to be practicable, FPM controller 162 preferably closesconcentrate recirculation control valve 124 and at least partially opensbrine outlet control valve 134, thus allowing brine to flow via brineoutlet 132 to a location outside of the at least one water treatmentsystem, thus reducing the system pressure to a pressure above theatmospheric pressure, which pressure exceeds the osmotic pressure of thefeed water at the feed side of module 100. The brine is all flushedthrough brine outlet 132 from the at least one water treatment system,while high pressure feed pump 102 continues to pump feed water to feedside of module 100, as shown in FIG. 5B. It is possible to increase theflow rate of pump 102 at this stage in order to speed the flushing ofthe brine.

Concentrate flow rate sensor 130 measures the cumulative volume of brineflowing from concentrate manifold 120, and thus measures when the fullflushing of the brine out of module 100 has been completed.

After fully flushing the brine from module 100, FPM controller 162reopens recirculation control valve 124 and closes brine outlet controlvalve 134, providing a liquid flow as shown in FIG. 5C, which may beidentical to the liquid flow illustrated in FIG. 5A, in which theoperation of high pressure pump 102 and the circulation pump 126supplies mixed feed water to module 100.

Reference is now made to FIGS. 6A-6D, which are simplified illustrationsof water flows in yet another embodiment of a water treatment system ofthe type shown in FIG. 1.

Prior to initiation of removal of the concentrate from module 100, brineoutlet control valve 134, auxiliary brine replacement control valve 140,auxiliary feed water control valve 148 and recycle conduit control valve156 are closed and recirculation control valve 124 is open. Theconcentrate from concentrate manifold 120 is directed back to the inputof feed manifold 114 via recirculation conduit 122 and recirculationcontrol valve 124, as shown by an arrow labeled CONCENTRATE (FIG. 1),representing the recirculation flow in the recirculation conduit 122. Infeed manifold 114, the concentrate is mixed with feed water, as shown byan arrow labeled MIXED (FIG. 1), representing the mixed flow in the feedmanifold 114. Thus, a mixed flow enters pressure vessels 110 for furthertreatment. The water flow for this stage is shown in a solid black linein FIG. 6A.

The feed pressure thereafter gradually increases, as the salinity of themixed liquid being supplied to the membrane elements 112 increases, andthe above-described recirculation process continues.

Once the concentration of the concentrate reaches a threshold, such as apredetermined pressure level, FPM controller 162 opens auxiliary brinereplacement control valve 140, closes recirculation control valve 124and opens auxiliary feed water control valve 148. Brine from concentratemanifold 120 flows through auxiliary brine replacement conduit 136,auxiliary brine replacement control valve 140 and auxiliary tank feedconduit 138 to auxiliary feed water tank 142.

The auxiliary feed water tank 142 is filled with feed water prior to theopening of brine replacement control valve 140, as describedhereinbelow. Brine entering the auxiliary feed water tank 142 drivesfeed water in it to feed manifold 114 via an auxiliary feed waterconduit 146 and an auxiliary feed water control valve 148.

The water flow for this stage is shown in a solid black line in FIG. 6B.

It is appreciated that the water in auxiliary feed water tank 142 may bemaintained at a pressure generally the same as the pressure of thebrine, such as by maintaining auxiliary opening brine replacementcontrol valve 140 in an open state as the pressure in the systemgradually increases. Alternatively, the water in the auxiliary feedwater tank 142 may be maintained at a pressure which is much lower thanthe pressure of the brine but above the atmospheric pressure byoperation of the auxiliary feed water pump 144 as described hereinbelow.

In the embodiment of FIGS. 6A-6D. FPM controller 162 preferablyincreases the flow rate of circulation pump 126 during flushing toachieve faster replacement of the brine from module 100 with feed waterfrom auxiliary feed tank 142, hence, reducing the time required for thebrine to be flushed from module 100 and replaced by feed water. Atypical graph of flow rate over time, as measured by concentrate flowrate sensor 130, located downstream of circulation pump 126, appears inan enlargement forming part of FIG. 6B, in which line 200 represents theflow rate over time.

Concentrate flow rate sensor 130 measures the cumulative volume of brineflowing from concentrate manifold 120 and thus measures the cumulativevolume of feed water entering feed manifold 114 via the auxiliary feedwater conduit 146 and the auxiliary feed water control valve 148, whichreplaces the brine in module 100.

After complete replacement of the brine with feed water in module 100,FPM controller 162 reopens recirculation control valve 124, closesauxiliary brine replacement control valve 140 and auxiliary feed watercontrol valve 148, and reduces the flow rate of circulation pump 126 tothe flow rate prior to opening concentrate recirculation control valve124, providing a liquid flow as shown in FIG. 6C, which may be identicalto the liquid flow illustrated in FIG. 6A, in which the operation ofhigh pressure pump 102 and the circulation pump 126 supplies mixed feedwater to module 100.

Thereafter, FPM controller 162 periodically activates auxiliary feedwater pump 144 and opens auxiliary brine outlet tank control valve 154to flush all brine from auxiliary feed water tank 142 through anauxiliary brine outlet 152 to a location outside of the at least onewater treatment system, and fill the auxiliary feed tank 142 with feedwater for further replacement of the brine in module 100 with feed wateras described hereinabove, as seen in FIG. 6D.

Following full replacement of brine with feed water in auxiliary feedwater tank 142, as measured by auxiliary flow rate sensor 150, FPMcontroller 162 closes auxiliary brine outlet tank control valve 154 andterminates operation of auxiliary feed water pump 144.

Reference in now additionally made to FIG. 2B, wherein periodicvariations in the feed water pressure during water treatment correspondto periodic variations in the salinity of the feed water entering module100, as measurable by a conductivity sensor (not shown), typicallylocated downstream of pressure sensor 108. As in FIG. 2A describedhereinabove, the y-axis represents the pressure variations in seawaterdesalination, and the x-axis represent the time. Dashed vertical line‘A’ represents the time where a threshold, such as a maximum feed waterpressure threshold, is reached

When the threshold is reached, pressure vessels 110 are still filledwith concentrate and both mixed osmotic pressure and mixed feed waterpressure continue to increase, until feed water enters the pressurevessels 110 replacing the concentrate therein. Typically, reaching thethreshold causes the system to begin the brine flushing process.

As described hereinabove, the mixed feed water osmotic pressure line 170represents the estimated osmotic pressure of mixed feed water at module100 inlet. Thus, when feed water from pump 102 is mixed with concentratefrom recirculation conduit 122, the mixed osmotic pressure graduallyincreases as seen in the gradual slope of line 170. Once a threshold,such as a salinity threshold or a pressure threshold, is reached thecontroller 162 preferably begins the flushing process. During theflushing process, concentrate is not recirculated back to feed manifold114, thus only feed water enters feed manifold 114 and the mixed osmoticpressure decreases sharply, as shown in the sharp decline in line 170.

Line 175 in FIG. 2B illustrates the behavior of the mixed feed waterpressure in the prior art, represented by the teaching of U.S. Pat. No.8,025,804. Line 180 illustrates the pressure being controlled by thecontroller such that the delta pressure needed for reverse osmosisdesalination process is maintained not only during the gradual increaseof mixed feed water pressure, when concentrate is being recirculatedback to feed manifold 114, but also at times of flushing the brine inpressure vessels 110 by feeding only feed water without recirculatedconcentrate. As seen in FIG. 2B, increasing of flow rate of circulationpump 126, vis-à-vis the flow rate of circulation pump 126 used in theexample of FIG. 2A, causes the mixed osmotic pressure line 170, as wellas the mixed feed water pressure line 180, to decrease even more rapidlythan in the example shown in FIG. 2A. In FIG. 2B, the increaseddifference between line 175 and line 180, vis-à-vis the differencebetween the two lines in FIG. 2A, illustrates the increased benefit ofoperation at lower pressures when the flow rate is increased, thussaving additional energy beyond the additional energy required tooperate the circulation pump 126 at a higher flow rate.

Reference is now made to FIGS. 7A-7D, which are simplified illustrationsof water flows in a further embodiment of a water treatment system ofthe type shown in FIG. 1.

Prior to initiation of removal of the concentrate from module 100, brineoutlet control valve 134, auxiliary brine replacement control valve 140,auxiliary feed water control valve 148 and recycle conduit control valve156 are closed and recirculation control valve 124 is open. Theconcentrate from concentrate manifold 120 is directed back to the inputof feed manifold 114 via recirculation conduit 122 and recirculationcontrol valve 124, as shown by an arrow labeled CONCENTRATE (FIG. 1),representing the recirculation flow in the recirculation conduit 122. Infeed manifold 114, the concentrate is mixed with feed water, as shown byan arrow labeled MIXED (FIG. 1), representing the mixed flow in the feedconduit 114. Thus, a mixed flow enters pressure vessels 110 for furthertreatment. The water flow for this stage is shown in a solid black linein FIG. 7A.

The feed pressure thereafter gradually increases as the salinity of themixed water being supplied to the membrane elements 112 increases, andthe above-described recirculation process continues.

Once the concentration of the concentrate reaches a threshold, such as apredetermined salinity level at which continued water treatment isdeemed not to be practicable, FPM controller 162 opens auxiliary brinereplacement control valve 140, closes recirculation control valve 124and opens auxiliary feed water control valve 148. The FPM controlleralso increases flow rate produced by circulation pump 126. Brine fromconcentrate manifold 120 flows through auxiliary brine replacementconduit 136, auxiliary tank feed conduit 138 and auxiliary brinereplacement control valve 140 to auxiliary feed water tank 142. Theauxiliary feed water tank 142 is filled with feed water prior to theopening of auxiliary brine replacement control valve 140, as describedhereinbelow. The brine enters the auxiliary feed water tank 142 anddrives feed water from tank 142 to feed manifold 114 via auxiliary feedwater conduit 146 and auxiliary feed water control valve 148. It isappreciated that water in auxiliary feed water tank 142 may be at thesame pressure as the pressure of the brine, such as by maintainingauxiliary brine replacement control valve 140 in an open state as thewater pressure in the system gradually increases. Alternatively, thewater in the auxiliary feed water tank 142 may be maintained at apressure which is much lower than the pressure of the brine but abovethe atmospheric pressure by operation of the auxiliary feed water pump144 as described hereinbelow.

In this embodiment, during flushing the FPM controller 162 preferablyopens recycle conduit control valve 156, resulting in a water flow froma location downstream of pump 102 to a location upstream of pump 102,preferably thorough a restrictor 160, thus lowering the feed waterpressure at manifold 114 to a pressure above atmospheric pressure, whichpressure exceeds the osmotic pressure of the feed water at the feed sideof module 100. The water flow for this stage is shown in a solid blackline in FIG. 7B.

A typical graph of flow rate over time, as measured by concentrate flowrate sensor 130, located downstream of circulation pump 126, appears inan enlargement forming part of FIG. 7B, in which line 200 represents theflow rate over time.

Concentrate flow rate sensor 130 measures the cumulative volume of brineflowing from concentrate manifold 120, and thus measures the cumulativevolume of feed water entering feed manifold 114 via the auxiliary feedwater conduit 146 and the auxiliary feed water control valve 148, whichreplaces the brine in module 100.

After complete replacement of brine with feed water in module 100, FPMcontroller 162 reopens recirculation control valve 124, and closesauxiliary brine replacement control valve 140, auxiliary feed watercontrol valve 148 and recycle conduit control valve 156, providing aliquid flow as shown in FIG. 7C, which may be identical to the liquidflow illustrated in FIG. 7A, in which the operation of high pressurepump 102 and the circulation pump 126 supplies mixed feed water tomodule 100.

Thereafter, the FPM controller 162 periodically activates the auxiliaryfeed water pump 144 and opens auxiliary brine outlet tank control valve154 to flush all brine from auxiliary feed water tank 142 through anauxiliary brine outlet 152 to a location outside of the at least onewater treatment system, and fill the auxiliary feed tank 142 with feedwater for further replacement of brine in module 100. This flow is shownin solid black lines in FIG. 7D.

Following full replacement of brine with feed water in auxiliary feedwater tank 142, as measured by auxiliary flow sensor 150, the FPMcontroller 162 closes auxiliary brine outlet tank control valve 154 andterminates operation of the auxiliary feed water pump 144.

Reference is now made to FIGS. 8A-8D, which are simplified illustrationsof water flows in yet another embodiment of a water treatment system ofthe type shown in FIG. 1.

Prior to initiation of removal of the concentrate from module 100, brineoutlet control valve 134, auxiliary brine replacement control valve 140,auxiliary feed water control valve 148 and recycle conduit control valve156 are closed and recirculation control valve 124 is open. Theconcentrate from concentrate manifold 120 is directed back to the inputof feed manifold 114 via recirculation conduit 122 and recirculationcontrol valve 124, as shown by an arrow labeled CONCENTRATE (FIG. 1),representing the recirculation flow in the recirculation conduit 122. Infeed manifold 114, the concentrate is mixed with feed water, as shown byan arrow labeled MIXED (FIG. 1), representing the mixed flow in the feedmanifold 114. Thus, a mixed flow enters pressure vessels 110 for furthertreatment. The water flow for this stage is shown in a solid black linein FIG. 8A.

The feed pressure thereafter gradually increases as the salinity of themixed water being supplied to the membrane elements 112 increases, andthe above-described recirculation process continues.

Once the concentration of the concentrate reaches a threshold, such as apredetermined salinity level at which continued water treatment isdeemed not to be practicable, FPM controller 162 opens auxiliary brinereplacement control valve 140, which is approximately at atmosphericpressure, thus reducing the water pressure within module 100 to apressure between the pressure of the concentrate at module 100 and thepressure of the feed water in the auxiliary feed tank 142.

Immediately thereafter, FPM controller 162 closes recirculation controlvalve 124 and opens auxiliary feed water control valve 148. Feed waterfrom auxiliary feed tank 142 flows via auxiliary feed water conduit 146and feed water control valve 144 to feed manifold 114, as shown in FIG.8B, thus supplying feed water to module 100 at a pressure above theosmotic pressure of the feed water and slightly higher than the pressurerequired for reverse osmosis to occur.

In the embodiment illustrated in FIGS. 8A-8D. FPM controller 162 alsoincreases the flow rate of circulation pump 126 during flushing toachieve faster replacement of the brine from module 100 with feed waterfrom auxiliary feed tank 142, hence, reducing the time required for thebrine to be flushed from module 100 and replaced by feed water. Atypical graph of flow rate over time, as measured by concentrate flowrate sensor 130, located downstream of circulation pump 126, appears inan enlargement forming part of FIG. 8B, in which line 200 represents theflow rate over time.

The water flow for this stage is shown in a solid black line in FIG. 8B.

Concentrate flow rate sensor 130 measures the cumulative volume of brineflowing from concentrate manifold 120 and thus measures the cumulativevolume of feed water entering feed manifold 114 via the auxiliary feedwater conduit 146 and the auxiliary feed water control valve 148, whichreplaces the brine in module 100.

After complete replacement of the brine with feed water in module 100.FPM controller 162 reopens recirculation control valve 124, closesauxiliary brine replacement control valve 140 and auxiliary feed watercontrol valve 148 and reduces the flow rate of circulation pump 126 tothe flow rate prior to opening concentrate recirculation control valve124, providing a liquid flow as shown in solid black lines in FIG. 8C,which may be identical to the liquid flow illustrated in FIG. 8A, inwhich the operation of high pressure pump 102 and circulation pump 126supplies mixed feed water to module 100.

Thereafter, the FPM controller 162 periodically activates the auxiliaryfeed water pump 144 and opens auxiliary brine outlet tank control valve154 to flush all brine from auxiliary feed water tank 142 through anauxiliary brine outlet 152 to a location outside of the at least onewater treatment system, and fill the auxiliary feed tank 142 with feedwater for further replacement of the brine in module 100. This flow isshown in solid black lines in FIG. 8D.

Following full replacement of brine with feed water in auxiliary feedwater tank 142, as measured by auxiliary flow rate sensor 150, the FPMcontroller 162 closes auxiliary brine outlet tank control valve 154 andterminates operation of the auxiliary feed water pump 144.

Reference is now made to FIGS. 9A-9D, which are simplified illustrationsof water flows in yet another embodiment of a water treatment system ofthe type shown in FIG. 1.

Prior to initiation of removal of the concentrate from module 100, brineoutlet control valve 134, auxiliary brine replacement control valve 140,auxiliary feed water control valve 148 and recycle conduit control valve156 are closed and recirculation control valve 124 is open. Theconcentrate from concentrate manifold 120 is directed back to the inputof feed manifold 114 via recirculation conduit 122 and recirculationcontrol valve 124, as shown by an arrow labeled CONCENTRATE (FIG. 1),representing the recirculation flow in the recirculation conduit 122. Infeed manifold 114, the concentrate is mixed with feed water, as shown byan arrow labeled MIXED (FIG. 1), representing the mixed flow in the feedconduit 114. Thus, a mixed flow enters pressure vessels 110 for furthertreatment. The water flow for this stage is shown in a solid black linein FIG. 9A.

The feed pressure thereafter gradually increases as the salinity of themixed water being supplied to the membrane elements 112 increases, andthe above-described recirculation process continues.

Once the concentration of the concentrate reaches a threshold, such as apredetermined salinity level at which continued water treatment isdeemed not to be practicable, FPM controller 162 at least partiallyopens brine outlet control valve 134, thus allowing brine to flow to viabrine outlet 132 to a location outside of the at least one watertreatment system, thus reducing the system pressure in module 100.

Additionally, in the embodiment shown in FIGS. 9A-9D, during flushingthe FPM controller 162 preferably opens recycle conduit control valve156, resulting in a water flow from a location downstream of pump 102 toa location upstream of pump 102, preferably thorough a restrictor 160,thus maintaining the feed water pressure at manifold 114 at a pressureabove atmospheric pressure, which pressure exceeds the osmotic pressureof the feed water at the feed side of module 100, as seen in FIG. 9B.

Immediately thereafter, FPM controller also opens auxiliary brinereplacement control valve 140, closes recirculation control valve 124and opens auxiliary feed water control valve 148. Brine from concentratemanifold 120 flows through auxiliary brine replacement conduit 136,auxiliary tank feed conduit 138 and auxiliary brine replacement controlvalve 140 to auxiliary feed water tank 142. The auxiliary feed watertank 142 is filled with feed water prior to the opening of auxiliarybrine replacement control valve 140, as described hereinbelow. The brineenters the auxiliary feed water tank 142 and drives feed water from tank142 to feed manifold 114 via auxiliary feed water conduit 146 andauxiliary feed water control valve 148. It is appreciated that water inauxiliary feed water tank 142 may be at the same pressure as thepressure of the brine, such as by maintaining auxiliary brinereplacement control valve 140 in an open state as the water pressure inthe system gradually increases. Alternatively, the water in theauxiliary feed water tank 142 may be maintained at a pressure which ismuch lower than the pressure of the brine but above the atmosphericpressure by operation of the auxiliary feed water pump 144 work asdescribed hereinbelow. The water flow for this stage is shown in a solidblack line in FIG. 9B.

Concentrate flow rate sensor 130 measures the cumulative volume of brineflowing from concentrate manifold 120 and thus measures when the fullflushing of the brine from module 100 has been completed. After fullyflushing the brine from module 100, FPM controller 162 reopensrecirculation control valve 124, and closes brine outlet control valve134, auxiliary brine replacement control valve 140, auxiliary feed watercontrol valve 148 and recycle conduit control valve 156, providing aliquid flow as shown in FIG. 9C, which may be identical to the liquidflow illustrated in FIG. 9A, in which the operation of high pressurepump 102 and circulation pump 126 supplies mixed feed water to module100.

Thereafter, the FPM controller 162 periodically activates the auxiliaryfeed water pump 144 and opens auxiliary brine outlet tank control valve154 to flush all brine from auxiliary feed water tank 142 through anauxiliary brine outlet 152 to a location outside of the at least onewater treatment system, and fill the auxiliary feed tank 142 with feedwater for further replacement of the brine in module 100. This flow isshown in solid black lines in FIG. 9D.

Following full replacement of brine with feed water in auxiliary feedwater tank 142, as measured by auxiliary flow sensor 150, the FPMcontroller 162 closes auxiliary brine outlet tank control valve 154 andterminates operation of the auxiliary feed water pump 144.

It is appreciated that in the embodiment shown in FIG. 9B, as describedhereinabove, a portion of the brine exits via brine outlet 132 and thusis not replaced with water from auxiliary feed water tank 142. Thevolume of water in module 100 may be replenished by increasing the flowrate of high pressure pump 102 or by any other suitable method.

Reference is now made to FIGS. 10A-10D, which are simplifiedillustrations of water flows in still another embodiment of a watertreatment system of the type shown in FIG. 1.

Prior to initiation of removal of the concentrate from module 100, brineoutlet control valve 134, auxiliary brine replacement control valve 140,auxiliary feed water control valve 148 and recycle conduit control valve156 are closed and recirculation control valve 124 is open. Theconcentrate from concentrate manifold 120 is directed back to the inputof feed manifold 114 via recirculation conduit 122 and recirculationcontrol valve 124, as shown by an arrow labeled CONCENTRATE (FIG. 1),representing the recirculation flow in the recirculation conduit 122. Infeed manifold 114, the concentrate is mixed with feed water, as shown byan arrow labeled MIXED (FIG. 1), representing the mixed flow in the feedconduit 114. Thus, the mixed flow enters pressure vessels 110 forfurther treatment. The water flow for this stage is shown in a solidblack line in FIG. 10A.

The feed pressure thereafter gradually increases as the salinity of themixed water being supplied to the membrane elements 112 increases, andthe above-described recirculation process continues.

Once the concentration of the concentrate reaches a threshold, such as apredetermined salinity level at which continued water treatment isdeemed not to be practicable, FPM controller 162 opens auxiliary brinereplacement control valve 140, which is approximately at atmosphericpressure, thus reducing the water pressure within module 100 to apressure between the pressure of the concentrate at module 100 and thepressure of the feed water in the auxiliary feed tank 142.

Immediately thereafter, FPM controller 162 closes recirculation controlvalve 124 and opens auxiliary feed water control valve 148. Brine fromconcentrate manifold 120 flows through auxiliary brine replacementconduit 136, auxiliary tank feed conduit 138 and auxiliary brinereplacement control valve 140 to auxiliary feed water tank 142. Theauxiliary feed water tank 142 is filled with feed water prior to theopening of auxiliary brine replacement control valve 140, as describedhereinbelow. The brine entering the auxiliary feed water tank 142 drivesfeed water in it to feed manifold 114 via auxiliary feed water conduit146 and auxiliary feed water control valve 148. It is appreciated thatwater in auxiliary feed water tank 142 may be maintained at a pressuregenerally the same as the pressure of the brine, such as by maintainingauxiliary brine replacement control valve 140 in an open state as thepressure in the system gradually increases. Alternatively, the water inthe auxiliary feed water tank 142 may be maintained at a pressure whichis much lower than the pressure of the brine but above the atmosphericpressure by operation of the auxiliary feed water pump 144 as describedhereinbelow.

Additionally, in the embodiment of FIGS. 10A-10D, during flushing theFPM controller 162 preferably opens recycle conduit control valve 156,resulting in a water flow from a location downstream of pump 102 to alocation upstream of pump 102, preferably thorough a restrictor 160,thus lowering the feed water pressure at manifold 114 to a pressureabove atmospheric pressure, which pressure exceeds the osmotic pressureof the feed water at the feed side of module 100.

Concentrate flow rate sensor 130 measures the cumulative volume of brineflowing from concentrate manifold 120 and thus measures the cumulativevolume of feed water entering feed manifold 114 via the auxiliary feedwater conduit 146 and the auxiliary feed water control valve 148, whichreplaces the brine in module 100.

After complete replacement of the brine with feed water in module 100,FPM controller 162 reopens recirculation control valve 124, and closesauxiliary brine replacement control valve 140, auxiliary feed watercontrol valve 148 and recycle conduit control valve 156, providing aliquid flow as shown in FIG. 10C, which may be identical to the liquidflow illustrated in FIG. 10A hereinabove.

Thereafter, the FPM controller 162 periodically activates the auxiliaryfeed water pump 144 and opens auxiliary brine outlet tank control valve154 to flush all brine from auxiliary feed water tank 142 through anauxiliary brine outlet 152 to a location outside of the at least onewater treatment system, and fill the auxiliary feed tank 142 with feedwater for further replacement of the brine in module 100. This flow isshown in solid black lines in FIG. 10D.

Following full replacement of brine with feed water in auxiliary feedwater tank 142, as measured by auxiliary flow sensor 150, the FPMcontroller 162 closes auxiliary brine outlet tank control valve 154 andterminates operation of the auxiliary feed water pump 144.

Reference is now made to FIGS. 11A-11D, which are simplifiedillustrations of water flows in another water treatment system of thetype shown in FIG. 1.

Prior to initiation of removal of the concentrate from module 100, brineoutlet control valve 134, auxiliary brine replacement control valve 140,auxiliary feed water control valve 148 and recycle conduit control valve156 are closed and recirculation control valve 124 is open. Theconcentrate from concentrate manifold 120 is directed back to the inputof feed manifold 114 via recirculation conduit 122 and recirculationcontrol valve 124, as shown by an arrow labeled CONCENTRATE (FIG. 1),representing the recirculation flow in the recirculation conduit 122. Infeed manifold 114, the concentrate is mixed with feed water, as shown byan arrow labeled MIXED (FIG. 1), representing the mixed flow in the feedconduit 114. Thus, a mixed flow enters pressure vessels 110 for furthertreatment. The water flow for this stage is shown in a solid black linein FIG. 11A.

The feed pressure thereafter gradually increases as the salinity of themixed water being supplied to the membrane elements 112 increases, andthe above-described recirculation process continues.

Once the concentration of the concentrate reaches a threshold, such as apredetermined salinity level at which continued water treatment isdeemed not to be practicable, FPM controller 162 opens auxiliary brinereplacement control valve 140 that is connected to auxiliary feed watertank 142 through auxiliary brine replacement conduit 136 and auxiliarytank feed conduit 138. In this embodiment, the water in auxiliary feedwater tank 142 is approximately at atmospheric pressure, thus openingauxiliary brine replacement control valve 140 reduces the water pressurewithin module 100 to a pressure between the pressure of the concentrateat module 100 and the pressure of the feed water in the auxiliary feedtank 142.

Immediately thereafter, FPM controller 162 closes recirculation controlvalve 124 and opens auxiliary feed water control valve 148. Brine fromconcentrate manifold 120 flows through auxiliary brine replacementconduit 136, auxiliary tank feed conduit 138 and auxiliary brinereplacement control valve 140 to auxiliary feed water tank 142. Theauxiliary feed water tank 142 is filled with feed water prior to theopening of auxiliary brine replacement control valve 140, as describedhereinbelow. The brine entering the auxiliary feed water tank 142 drivesfeed water from auxiliary feed tank 142 via auxiliary feed water conduit146 and auxiliary feed water control valve 148 to feed manifold 114,thus supplying feed water to module 100 at a pressure above the osmoticpressure of the feed water and not much higher than the pressurerequired for a reverse osmosis to occur.

In this embodiment, during flushing, the FPM controller 162 preferablyalso opens recycle conduit control valve 156, resulting in a water flowfrom a location downstream of pump 102 to a location upstream of pump102, preferably through a restrictor 160, thus lowering the feed waterpressure at manifold 114 to a pressure above atmospheric pressure, whichpressure exceeds the osmotic pressure of the feed water at the feed sideof module 100. In this embodiment illustrated in FIGS. 11A-11D, FPMcontroller also increases the flow rate produced by circulation pump 126during flushing to achieve a faster replacement of the brine from module100 with feed water from auxiliary feed tank 142, hence, reducing thetime required for the brine to be flushed from module 100 and replacedby feed water. A typical graph of flow rate over time, as measured byconcentrate flow rate sensor 130, located downstream of circulation pump126, appears in an enlargement forming part of FIG. 11B, in which line200 represents the flow rate over time.

The water flow for this stage is shown in a solid black line in FIG.11B.

Concentrate flow rate sensor 130 measures the cumulative volume of brineflowing from concentrate manifold 120 and thus measures the cumulativevolume of feed water entering feed manifold 114 via the auxiliary feedwater conduit 146 and the auxiliary feed water control valve 148, whichreplaces the brine in module 100.

After complete replacement of brine with feed water in module 100, FPMcontroller 162 reopens recirculation control valve 124, closes auxiliarybrine replacement control valve 140, auxiliary feed water control valve148 and recycle conduit control valve 156, and reduces the flow rate ofcirculation pump 126 to the flow rate prior to opening recirculationcontrol valve 124, providing a liquid flow as shown in solid black linesin FIG. 11C, which may be identical to the liquid flow illustrates inFIG. 11A, in which the operation of high pressure pump 102 andcirculation pump 126 supplies water to module 100.

Thereafter, the FPM controller 162 periodically activates the auxiliaryfeed water pump 144 and opens auxiliary brine outlet tank control valve154 to flush all brine from auxiliary feed water tank 142 through anauxiliary brine outlet 152 to a location outside of the at least onewater treatment system, and fill the auxiliary feed tank 142 with feedwater for further replacement of brine in module 100. This flow is shownin a solid black line in FIG. 11D.

Following full replacement of brine with feed water in auxiliary feedwater tank 142, as measured by auxiliary flow sensor 150, the FPMcontroller 162 closes auxiliary brine outlet tank control valve 154 andterminates operation of the auxiliary feed water pump 144.

It will be appreciated by persons skilled in the art that the presentinvention is not limited by what has been specifically shown anddescribed hereinabove. Rather the scope of the invention includes bothcombinations and sub-combinations of features described and shownhereinabove as well as modifications thereof which would occur topersons reading the foregoing description and which are not in the priorart.

1. A liquid treatment system for treatment of feed liquid, the liquidtreatment system comprising: at least one liquid treatment modulecomprising at least one membrane and in communication with a liquidinlet, with a concentrate outlet, and with a permeate outlet; a highpressure pump which normally maintains a fixed output liquid volumenotwithstanding variations in liquid pressure at an outlet of the highpressure pump, the high pressure pump exhibiting an energy consumptionthat is a function of the variations in liquid pressure at the outlet ofthe high pressure pump, the high pressure pump being operative topressurize a feed liquid to be supplied to the at least one liquidtreatment module via said liquid inlet; a circulation pump forcirculating a concentrate from said concentrate outlet to said liquidinlet for the pressurized feed liquid to be mixed with the concentrate,to result into a mixed liquid to be supplied to said to the at least oneliquid treatment module via said liquid inlet; and a controllerconfigured for: controlling the high pressure pump; monitoring theliquid pressure downstream from the high pressure pump; determining thatthe liquid pressure downstream from the high pressure pump has reached apredetermined high pressure threshold representing exceedance of asalinity threshold of the concentrate; and immediately after saiddetermination, lowering the liquid pressure downstream from the highpressure pump to a level which exceeds an osmotic pressure of the feedliquid, thereby immediately reducing the energy consumption of the highpressure pump.
 2. The liquid treatment system of claim 1, wherein thecontroller is configured for lowering the liquid pressure downstreamfrom the high pressure pump to a pressure below osmotic pressure of themixed liquid at said liquid inlet at the time of the exceedance.
 3. Theliquid treatment system of claim 1, further comprising: a liquidpressure reducing valve at a brine outlet, wherein the at least oneliquid treatment module is in communication with the brine outlet; aliquid feed tank; and a recycle conduit control valve which provides apressure reducing backflow liquid path from the outlet of the highpressure pump to an inlet of the high pressure pump, the backflow liquidpath bypassing the high pressure pump; wherein for lowering the liquidpressure downstream from the high pressure pump, the controller isconfigured to perform at least one of the following operations: openingsaid liquid pressure reducing valve, thereby removing said concentratefrom said liquid treatment system; stopping said circulation andincreasing a liquid volume output of the circulation pump from volumeoutput of the circulation pump when the circulation pump circulates saidconcentrate from the at least one liquid treatment module to the liquidinlet at times other than upon and immediately following the exceedance;equilibrating liquid pressures between a liquid pressure inside the atleast one liquid treatment module and inside said liquid feed tank; andopening said recycle conduit control valve.
 4. The liquid treatmentsystem of claim 1, further comprising: wherein the controller isconfigured for lowering the liquid pressure downstream from the highpressure pump to a pressure below osmotic pressure of the mixed liquidat said liquid inlet at the time of the exceedance; a liquid pressurereducing valve at a brine outlet, wherein the at least one liquidtreatment module is in communication with the brine outlet; a liquidfeed tank; and a recycle conduit control valve which provides a pressurereducing backflow liquid path from the outlet of the high pressure pumpto an inlet of the high pressure pump, the backflow liquid pathbypassing the high pressure pump; wherein for lowering the liquidpressure downstream from the high pressure pump, the controller isconfigured to perform at least one of the following operations: openingsaid liquid pressure reducing valve, thereby removing said concentratefrom said liquid treatment system; stopping said circulation andincreasing a liquid volume output of the circulation pump from volumeoutput of the circulation pump when the circulation pump circulates saidconcentrate from the at least one liquid treatment module to the liquidinlet at times other than upon and immediately following the exceedance;equilibrating liquid pressures between a liquid pressure inside the atleast one liquid treatment module and inside said liquid feed tank; andopening said recycle conduit control valve.
 5. The liquid treatmentsystem of claim 1, further comprising: a liquid pressure reducing valveat a brine outlet, wherein the at least one liquid treatment module isin communication with the brine outlet; a liquid feed tank; and arecycle conduit control valve which provides a pressure reducingbackflow liquid path from the outlet of the high pressure pump to aninlet of the high pressure pump, the backflow liquid path bypassing thehigh pressure pump; wherein for lowering the liquid pressure downstreamfrom the high pressure pump, the controller is configured to perform atleast one of the following operations: opening said liquid pressurereducing valve, thereby removing said concentrate from said liquidtreatment system; stopping said circulation and increasing a liquidvolume output of the circulation pump from volume output of thecirculation pump when the circulation pump circulates said concentratefrom the at least one liquid treatment module to the liquid inlet attimes other than upon and immediately following the exceedance;equilibrating liquid pressures between a liquid pressure inside the atleast one liquid treatment module and inside said liquid feed tank; andopening said recycle conduit control valve; wherein for lowering theliquid pressure downstream from the high pressure pump, the controlleris configured for: removing said concentrate from the liquid treatmentsystem; and reducing pressure of the mixed liquid in the at least oneliquid treatment module by at least one of the following operations:opening a pressure reducing valve downstream from the high pressurepump; stopping said circulation and increasing a liquid volume output ofthe circulation pump from volume output of the circulation pump when thecirculation pump circulates said concentrate from the at least oneliquid treatment module to the liquid inlet at times other than upon andimmediately following the exceedance; and passing the pressurized feedliquid from downstream from the high pressure pump to upstream from thehigh pressure pump.
 6. The liquid treatment system of claim 1, whereinfor lowering the liquid pressure downstream from the high pressure pump,the controller is configured for: removing said concentrate from theliquid treatment system; and reducing pressure of the mixed liquid inthe at least one liquid treatment module by at least one of thefollowing operations: opening a pressure reducing valve downstream fromthe high pressure pump; stopping said circulation and increasing aliquid volume output of the circulation pump from volume output of thecirculation pump when the circulation pump circulates said concentratefrom the at least one liquid treatment module to the liquid inlet attimes other than upon and immediately following the exceedance; andpassing the pressurized feed liquid from downstream from the highpressure pump to upstream from the high pressure pump.
 7. The liquidtreatment system of claim 1, wherein the controller is configured forlowering the liquid pressure downstream from the high pressure pump to apressure below osmotic pressure of the mixed liquid at said liquid inletat the time of the exceedance; wherein for lowering the liquid pressuredownstream from the high pressure pump, the controller is configuredfor: removing said concentrate from the liquid treatment system; andreducing pressure of the mixed liquid in the at least one liquidtreatment module by at least one of the following operations: opening apressure reducing valve downstream from the high pressure pump; stoppingsaid circulation and increasing a liquid volume output of thecirculation pump from volume output of the circulation pump when thecirculation pump circulates said concentrate from the at least oneliquid treatment module to the liquid inlet at times other than upon andimmediately following the exceedance; and passing the pressurized feedliquid from downstream from the high pressure pump to upstream from thehigh pressure pump.
 8. The liquid treatment system of claim 1, furthercomprising: wherein for lowering the liquid pressure downstream from thehigh pressure pump, the controller is configured for: removing saidconcentrate from the liquid treatment system; and reducing pressure ofthe mixed liquid in the at least one liquid treatment module by at leastone of the following operations: opening a pressure reducing valvedownstream from the high pressure pump; stopping said circulation andincreasing a liquid volume output of the circulation pump from volumeoutput of the circulation pump when the circulation pump circulates saidconcentrate from the at least one liquid treatment module to the liquidinlet at times other than upon and immediately following the exceedance;and passing the pressurized feed liquid from downstream from the highpressure pump to upstream from the high pressure pump; a flow restrictorarranged in parallel with the high pressure pump; and wherein saidpassing the pressurized feed liquid from downstream from the highpressure pump to upstream from the high pressure pump includes passingthe pressurized feed liquid via said flow restrictor.
 9. The liquidtreatment system of claim 1, further comprising: a recirculation controlvalve disposed between said concentrate outlet and said liquid inlet;wherein said circulation pump is configured for circulating theconcentrate via the recirculation control valve, and the systemcontroller is configured for, immediately after said determination,closing the recirculation control valve.